1. Field of the Invention
The present invention relates to bridge structure monitoring and safety evaluation technology applicable for bridge maintenance management and more particularly, to such a bridge monitoring and safety evaluation method, which employs specific vibration measuring and analysis techniques to analyze the structural stability of a bridge and then to evaluate the life cycle of the structure of the bridge so as to further achieve a bridge health inspection and long-term bridge behaviors monitoring analysis.
2. Description of the Related Art
Most rivers in Taiwan have the characteristics of steep slope and quick water. Under the impact of heavy rainfall or typhoon with flood, river beds are seriously destroyed, causing exposure of the piers and foundation of the bridges. Continuous erosion results in tilt and damage of the bridge pier foundations or even bridge collapse.
Known bridge erosion studies and prevention techniques are created based on one single technique or one single physical method. More particularly, most conventional bridge foundation erosion examining and monitoring methods employ ultrasonic waves, gravity and fiber optical measuring techniques to detect the depth of erosion, water depth and other environmental conditions. For example, Taiwan Utility Model Patent Application No. 89203602 discloses a gravity type erosion measurement device, which uses a rope to extend a weight along a fixed sleeve to the erosion surface and to measure the depth of erosion by means of letting off and taking up the rope. Taiwan Utility Model Patent Application No. 91204412 discloses an optical fiber measuring technique that provides a riverbed sediment monitoring device, which uses a flexible rod member carrying a fiber bragger grating sensor therein for erecting in the riverbed. When the riverbed reaches a predetermined elevation, the fiber bragger curves, and a related physical amount of variation indicative of the erosion depth is obtained through an analyzer. Taiwan Invention Patent Application No. 94102692, entitled “Water guide type bridge erosion prevention device”, teaches the use of water guide means to guide water upwards or sideways, preventing down flow of water in washing away riverbed. The washout prevention effect reaches 50%-70%. Taiwan Invention Patent No. 96123632 discloses “Monitoring device for monitoring bridge foundation and riverbed erosion, remote automatic monitoring system and bridge with automatic monitoring function”. This invention uses a gravity survey rod to measure the depth of erosion and a protective sleeve to enhance the strength against impact of drifting objects, and finally uses a signal pickup unit to pick up the sliding distance between the gravity survey rod and the protective sleeve and to convert the signal into a digital signal for transmission to a remote control center.
The aforesaid prior art inventions have the following technical blind spots:
1. The objects to be measured are the environmental conditions around the bridge, such as the erosion depth and water depth. These environmental conditions are indirect conditions for structural stability analysis. Simply obtaining the real time data of these environmental conditions still cannot rapidly and accurately known the safety conditions of the bridge structure.
2. In actual practice, the security and durability of the devices of the prior art techniques are doubtful. The devices of the prior art techniques need to be dipped in water or embedded in the riverbed. They may be unable to effectively perform the measurement or to survive under the impact of quick water, rocks, drifting objects and down flow of water.
3. Because the objects to be measured are environmental conditions, the aforesaid prior art techniques cannot get the bridge structure long-term variational trend or effectively respond to the actual bridge structure critical condition after several catastrophe events.